Many kinds of heat sensitive recording materials applying reactions of leuco chromogens with color developing materials have been commonly utilized in recording paper for output recorder of for facsimile and various instruments.
Because, it has been desired as character of the heat sensitive material to be higher sensitive for color evolution, higher whiteness of the background and higher stability of the colored image and toughness of the background concurrently, many kinds of sensitizers and stabilizers have been developed.
Sufficient material for such functions has never been found. Some compounds which were resemble to those of the present invention represented by general formula (I) but involved alkyl group such as isopropyl and glycidyl group at R.sup.1 in the structure were known as adjuvant for heat sensitive recording materials. (Japanese Patent Application (unexamined) Sho 62-164579 (1987)).
The resemble compounds, above mentioned, to those in the invention have been used as storage stabilizer for color image, but their functions have been insufficient. Furthermore, they have toxicological problem such as mutagenicity. Therefore, their disadvantages in the manufacture and marketing have been in very severe circumstances according to the legal control. The purpose of the present invention is to provide a heat sensitive material with outstanding background whiteness, storage stability of the background and of the color image but without the toxicological problems above mentioned.